Simple explosive train arming method



Oct. 3, 196-1 J. SAVITT 3,002,456

v SIMPLE EXPLOSIVE TRAIN ARMING METHOD Filed Jan. 26, 1956 2 Shee ts-Sheet 1 FIG.1.

INVENTOR JACOB SAVITT BY W' A ORNEY Oct. 3, 1961 I J. SAVITT 3,002,456

SIMPLE EXPLOSIVE TRAIN ARMING METHOD Filed Jan. 26, 1956 2 Sheets-Sheet 2 II" I] DISTANCE FROM CHARGE SURFACE FIG.6.

aanssaad INVENTOR JACOB SAVITT BY (7%.; Wd

ATTORNEY 3,002,456 SIMPLE EXPLOSIVE TRAIN AiRMlNG METHOD Jacob Savitt, Park Forest, 11]., assignor to the United States of America as represented by the Secretary of the Navy Filed Jan. 26, 1956, Ser. No. 561,692 7 Claims. (Cl. 102-70) (Granted under Title 35, U8. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to an arming device for an explosive Weapon and more particularly to an arming mechanism for explosive ordnance in which a water shield is employed to prevent premature explosion of the device by detonator fragments and reaction products in the event that the detonator is fired before the device is armed.

In certain systems heretofore devised arming was achieved by filling a normally air filled cavity between the detonator and the explosive with water whereby the matching acoustic impedance of the water is employed to transmit the explosive shock to the acceptor charge with a degree of efliciency suflicient to fire the charge, the charge being disposed at a distance from the detonator suflicient to prevent firing thereof in response to actuation of the detonator when the cavity therebetween is air filled.

Such a system is disclosed and claimed in the copending application for Explosive Train Arming Device by Dick A. Plank, Serial No. 552,954, filed December 13,

While such systems have been found to be satisfactory in preventing premature explosion of the acceptor charge (booster) by the donor charge (detonator) in response to the pressure wave set up by the detonator upon actuation thereof, by reason of the rapid attenuationof the explosive force within the air filled cavity intermediate the detonator and the acceptor charge as a result of mismatch between the acoustic'impedance of the airand the explosive agents, it has been found that the explosion of a detonator in addition to setting up this rapidly attenuating pressure wave also carries-with it certain explosion products and fragments of the detonator shell. Under certain conditions of service, there is a remote possibility that these explosion by-products and fragments of the detonator shell might cause premature ignition of the explosive charge when the cavity was air filled.

The present invention provides new and improved means of preventing ignition of the acceptor charge by flying fragments or explosive by-products when the device is in an unarmed condition by providing a shield or liquid barrier between the donor and acceptor elements such that the primary initiating agent of the acceptor is only a shock wave. When the detonator cavity is air filled this shock wave is attenuated sufiiciently to prevent initiation of the detonation of the acceptor by the time it has traveled the distance to the acceptor. When the cavity is filled with water, however, the explosive shock is propagated through the water to the acceptor explosive with sufiicient intensity to initiate detonation thereof.

According to another form of the invention this result is achieved by employing an L-shaped cavity with the donor and acceptor element disposed at the ends thereof in such manner that the flying detonator fragments and explosive products are prevented from impinging on the aweptor exrlesiveeehenethe eavityeieairefih enga emenrwith steeve ii': nrrexpiosive charge indi unarmed condition. With this arrangement the water 3,002,456 Patented Oct. 3, 1961 barrier is not required. When the L-shaped cavity is filled with water the device is armed and the pressure wave is transmitted to the acceptor explosive with suflicient force to initiate the firing thereof.

One of the objects of the present invention is the pro vision of new and improved means for increasing the safety factor of an arming device for an explosive weapon.

Another object is the provision of new and improved means for filtering out detonator fragments and explosive products from the explosive wave of a detonator as the detonator is fired.

Still another object is the provision of a water barrier for preventing impingement of detonator fragments and explosive products against an explosive acceptor as the detonator is fired.

A further object resides in the provision of new and improved means for retaining a quantity of liquid in the explosive path of the detonator adjacent an air filled cavity sufiicient to filter out detonatorfragments and explosive products from the explosive wave as the detonator operates.

Still other objects and advantages will be apparent from the following description taken in connection with the accompanied drawings, in which:

FIG. 1 is a view in section of the arming device of the present invention in accordance with a preferred embodiment thereof;

FIG. 2 is a fragmentary view partly in section of the device of FIG. 1 applied to a marine mine.

FIG. 3 is a graphic representation of attenuation of pressure of an explosive wave transmitted through air and through water respectively;

FIG. 4 is a graphic representation of the device in safe condition;

FIG. 5 is a graphic showing of the device in an armed' condition;

FIG. 6 illustrates graphically a structural arrangement of the donor and acceptor elements to achieve the added safety feature in accordance with an alternative form of the invention; and

. FIG. 7 is a view similar to FIG. 6 with the device in 'an armed condition.

Referring now to the drawings for a more complete understanding of the invention and more particularly to 'FIG. 1 thereof there is shown thereon the arming and safety device of the present invention indicated by the numeral 10, the device comprising a cylindrical member 11 composed of metal suitable for the purpose such for example as brass, steel or the like, secured in any suitable manner to a support member 12. The member 12 is tapped or otherwise formed to receive and support an electroresponsive detonator 13. A metal sleeve 14 is fitted within the cylinder 11 and encircles the detonator 13 substantially as shown. A strip of cellophane or Scotchtape '15 abuts the end of the sleeve 14 and is held thereagainst by a sleeve 16. The space within the sleeve 16 is filled with a liquid such, for example, as water and a disc of cellophane or Scotch tape 17 is employed .to seal the water within the sleeve 16. A sleeve 18 is employed to hold the disc 17 in sealed relation with the sleeve 16. The sleeve 18 is also liquid filled, the liquid being retained therein by a cellophane or Scotch tape disc 19. Abutting the disc 19 is an elongated cylindrical sleeve 21 having a pair of apertures 22 and 23 disposed therein substantially as shown and in registration with complementary apertures 24 and 25 respectively formed in the cylinder 11. An additional sleeve 26 having a quantity of acceptor explosive 27', such, for example, as tetryl, compressed therein at 4,000 psi. is fitted within cylinder 11 in abutting cated by the numeral 28 is arranged in abutting relation with the acceptor explosive 27 and adapted to be ignited thereby.

Within aperture 24 is secured a fitting 29 for establishing communication to a duct 31 connected thereto and in a like manner a duct 32 is connected by fitting 33 to aperture 25 for a purpose which will be more clearly apparent as the description proceeds.

The detonator 13 is preferably of the electro-responsive type adapted to be fired by a firing signal received over the pair of firing leads 34 connected thereto. The leads 34 are electrically connected to any type of firing mechanism suitable for the purpose such, for example, as the firing mechanism disclosed in the patent application of Dick A, Plank aforesaid.

Referring now to FIG. 2 on which is shown a mine indicated generally by the numeral 35, the arming and safety device of the present invention may be secured in any suitable manner as by the bolts 36 to the interior of the mine casing. The upper portion of air filled chamber 37 within the sleeve 21 is in communication with a well 33 disposed at the upper portion of the mine casing when the mine is at rest and in like manner the lower portion of chamber 37 is in communication as by the duct 32 to a well 39 formed on a lower portion of the mine casing. Within each of the wells 38 and 39 respectively is located a soluble washer 40 in such manner as to exclude water entry into the ducts 31 and 32 until the washer has dissolved, as is well known in the art to which the invention pertains.

The operation of the device when employed, for example, in the mine of FIG. 2 will now be described. Let it be assumed, by way of example, that the chamber 87 is air filled, the ducts 31 and 32 are sealed and the mine is planted within the water. When a predetermined period of time has elapsed the salt washers within the wells 33 and 39 are dissolved and chamber 37, FIG. 1, fills with water. The device is now armed. As chamber 37 is filled with water, the cavity between detonator 13 and acceptor explosive 27 is water filled thereby providing a shock transmitting medium of sufficiently high degree of efficiency to cause the acceptor charge 27 to be fired by detonator 13 as a firing impulse is received over conductors 34 thereby actuating booster charge 20 and firing the mine.

In the event, however, that a firing impulse should be applied to conductors 34 before the salt washers have dissolved, the air filledchamber 37, by reason of mismatch of the acoustic impedance transmitting characteristic of the air, causes the explosive shock to be attenuated sufiiciently to prevent actuation of the acceptor explosive 27. The water barrier within sleeves 17 and 18, it should be noted, eflfectively'filters out from the explosive wave the explosion by-products and detonator fragments thereby preventing any possibility of initiation of the operation of the acceptor explosive 27'.

On FIG. 3 is shown the curves 41 and 42 respectively the correlation between the pressure from the charge surface 4-3 as the distance therefrom Varies, curve 41 illustrating the variation inpressure when air surrounds the explosive or is employed in the cavity between the explosive and the. acceptor and the curve 42 illustrating the variation in pressure when water is employed in lieu of air in the cavity. From these curves it should be noted that whereas the initial pressure at a short distance from the explosive surface is higher when air is employed in lieu of water, this pressure attenuates rapidly and falls below the value of the pressure in a water medium at a distance X from the charge surface. The'degree of pressure required to fire the acceptor explosive 27 is indicated by the dot-dash line 44 and an acceptor explosive disposed at a greater distance from detonator than Y, will be fired only when the cavity 37 is water filled. This condition is shovm in graphic form on FIG. 4 in which the air filled cavity 37 disposed between the detonator 13 and the acceptor explosive 27 is air filled and the device y 4 is in a safe or unarmed condition. When the chamber 37 is water filled, FIG. 5, the device is armed.

On FIG. 6 is shown an arrangement in which the detonator 13 and acceptor explosive 27 are arranged at opposite ends of an L-shaped cavity. With this arrangementrthe water barrier of FIG. 1 is not required to prevent'the explosive product and detonator fragments 'fiom impinging directly against the acceptor explosive. As detonator 13 is fired the fragments of the detonator shell and the explosive products are forcibly driven against the wall 45 of the cavity and thus are inetfective tov ignite the acceptor charge 27 when the cavity is air filled, FIG. 6. On the other hand, when the cavity is water filled, FIG. 7, the force of the explosive wave caused by the operation of detonator 13 is sufficient to actuate the acceptor explosive.

A structural configuration for the device of FIG. 1 has been found to be satisfactory when the cylinders 01' sleeves 14, 16, 18, 21 and 26 are made of brass with an outside diameter of 1 inch and an inside diameter of .200 inch. The length of cylinder 14, as illustrated, is just sufi'icient to allow the Scotch tape or cellophane 15 to be extended thereacross in substantial abutting relation with the end of detonator 13. The length of cylinders 16 and 18 are .250 inch and .500 inch respectively. The length of sleeves 21 and 26 are each 1 inch. The detonator 13 is filled with PETN at 10,000 p.s.i. and the acceptor explosive 27 is composed of tetryl pressed within the sleeve26 at a pressure of 4.000 p.s.i.

Whereas in the foregoing description the dimensions of a structural embodiment of the invention which gives. satisfactory results has been disclosed, it will be understood that this is by way of illustration only and other dimensions may be employed, if desired, and other explosives for the detonator and acceptor may be employed without departing from the spirit and scope of the invention. Furthermore, whereas the water barrier has been described with reference to a position within the device immediately adjacent the detonator and the chamber 37 has been shown arranged next to the acceptor explosive, it will be understood, if desired, that the positions of the water barrier and chamber 37 may be transposed without departing from the present invention. Whereas the water barrier has been illustrated as comprising two sections separated by the disc 17, it will be understood that, if desired, the disc 17 may be omitted and the water barrier may be contained within a single chamber. Furthermore, whereas the invention has been described with particular reference to water as the liquid barrier between the detonator and the acceptor explosive, it will be understood that other liquids, such, for example, as oil, glycerin and the like may be employed in lieu thereof.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. An arming device comprising a casing having a bore therein, a donor explosive charge and an acceptor explosive charge disposed within said bore in mutual spaced relationship, means forming first and second chambers interposed within the bore and between said donor and acceptor charges, said second chamber being normally air filled, a quantity of liquid within said first chamber, and means for admitting liquid into said second chamber whereby the device is armed.

2. An arming device for an explosive weapon comprisinga rig-id elongated tubular structure, an electroresponsive detonator secured within one end of said structure, an acceptor explosive disposed within the other end of the structure, a quantity of liquid sealed said structure intermediate said detonator and explosive and filling a fractional portion of the space therebetween, the remainder of said space being air filled when the device is unarmed, and means for filling the remainder of said space with liquid thereby to arm the device.

3. An arming device for explosive ordnance comprising a :body member having an elongated bore therein, a detonator disposed within an end portion of said bore, an acceptor charge disposed within the other end portion of said bore, means forming a chamber within the bore adjacent said detonator within which is disposed a quantity of liquid sufiicient to fill the chamber, an air filled chamber within the bore intermediate said first named chamber and the acceptor charge, and means for introducing a quantity of liquid within said second chamber sufiicient to fill the chamber and thereby increase the acoustic impedance of the shock transmitting medium within said bore sufficiently to cause ignition of the acceptor charge in response to firing to said detonator.

4. In an arming device for an exposive weapon comprising a rigid elongated structure having a bore therein, an electroresponsive detonator secured within one end of said bore, an acceptor exposive charge disposed within the other end of the bore in spaced relation with respect to said detonator, means forming a water barrier disposed transverse to said bore and coextensive therewith throughout a fractional portion of the distance between said detonator and charge whereby combustion products and detonator fragments are prevented from impinging on said charge as the detonator is actuated while the device is unarmed, means forming an air chamber within said bore of sufi'icient size to prevent ignition of the charge by a pressure wave as the detonator is fired while the chamber is air filled, and means for admitting a liquid to said chamber thereby to arm the device by an increase in the acoustic impedance thereof sufiiciently for the charge to be fired by a pressure wave received from the detonator as the detonator is actuated.

5. In an arming device for an explosive weapon comprising a rigid elongated body having a bore therein, a detonator disposed within one end of said bore, an acceptor charge disposed within the other end of said bore, the space between said detonator and charge being normally filled with air thereby to provide a mismatch of acoustic impedance of the shock transmitting medium sufiicient to prevent firing of said charge by a pressure wave received from said detonator, means for filling said space with liquid thereby to increase the shock transmission from the detonator to the charge sufliciently to fire the charge as the detonator operates, and safety means comprising a liquid barrier disposed within said bore and filling a small portion of the space between said detonator and charge for preventing firing of the charge by combustion products and detonator fragments when the detonator is actuated while the remainder of said space is air filled.

6. In a device of a character disclosed for firing an acceptor charge, in combination, detonating means, tubular structure for supporting said detonating means in spaced relation with respect to said charge at a distance sufiicient to prevent firing of the charge by a pressure wave as the detonator is actuated While the shock transmitting medium therebetween is air filled, means for replacing the air shock transmitting medium by a liquid whereby the shock transmission of the wave of pressure is sufficient to fire the charge, and means for preventing explosive products and detonator fragments from impinging on the charge prior to the change in the shock transmitting medium from air to water, said last named means comprising a water barrier disposed transversely intermediate said detonator and charge for a small fractional portion of the distance therebetween.

7. An arming device for an explosive weapon comprising a rigid L-shaped tube-like structure and an electroresponsive detonator secured within one end of said structure, an acceptor explosive disposed the other end of the structure, said structure having the space between said detonator and explosive normally filled with air, the distance between the detonator and explosive being sufilcient to prevent firing of the explosive by the pressure wave received from the detonator when the space therebetween is air filled, means for filling said space with a liquid thereby to improve the shock transmission characteristic of the wave transmitting medium suificiently to cause the explosive to be fired by a pressure wave received from the detonator as the detonator is actuated While the space is liquid filled, said L-shaped structure preventing impingement of explosion products and detonator fragments against said explosive as the detonator is fired while said space is air filled thereby preventing premature explosion of the explosive as a result of such impingement.

References Cited in the file of this patent UNITED STATES PATENTS 2,660,952 Mohaupt Dec. 1, 1953 

